1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to a piezoelectric ink-jet printhead made on a silicon substrate, and a method for manufacturing the same using a micromachining technology.
2. Description of the Related Art
In general, ink-jet printheads are devices for printing a predetermined color image by ejecting small droplets of printing ink at a desired position on a recording sheet. Ink ejection mechanisms of an ink-jet printer are generally categorized into two different types: an electro-thermal transducer type (bubble-jet type), in which a heat source is employed to form bubbles in ink thereby causing an ink droplet to be ejected, and an electro-mechanical transducer type, in which an ink droplet is ejected by a change in ink volume due to deformation of a piezoelectric element.
A typical structure of an ink-jet printhead using an electro-mechanical transducer is shown in FIG. 1. Referring to FIG. 1, an ink reservoir 2, a restrictor 3, an ink chamber 4, and a nozzle 5 for forming an ink passage are formed in a passage forming plate 1. A piezoelectric actuator 6 is provided on the passage forming plate 1. The ink reservoir 2 stores ink supplied from an ink container (not shown), and the restrictor 3 is a passage through which ink is supplied to the ink chamber 4 from the ink reservoir 2. The ink chamber 4 is filled with ink to be ejected. The volume of the ink chamber 4 is varied by driving the piezoelectric actuator 6, thereby a variation in pressure for ink ejection or in-flow is generated. The ink chamber 4 is also referred to as a pressure chamber.
The passage forming plate 1 is formed by cutting a plurality of thin plates formed of ceramics, metals, or plastics, forming a part of the ink passage, and then stacking the plurality of thin plates. The piezoelectric actuator 6 is provided above the ink chamber 4 and includes a piezoelectric thin plate stacked on an electrode for applying a voltage to the piezoelectric thin plate. As such, a portion of the passage forming plate 1 forming an upper wall of the ink chamber 4 serves as a vibration plate 1a to be deformed by the piezoelectric actuator 6.
The operation of a conventional piezoelectric ink-jet printhead having the above structure will now be described.
If the vibration plate 1a is deformed by driving the piezoelectric actuator 6, the volume of the ink chamber 4 is reduced. As a result, due to a variation in pressure in the ink chamber 4, ink in the ink chamber 4 is ejected through the nozzle 5. Subsequently, if the vibration plate 1a is restored to an original state by driving the piezoelectric actuator 6, the volume of the ink chamber 4 is increased. As a result, due to a variation in a pressure in the ink chamber 4, ink stored in the ink reservoir 2 is supplied to the ink chamber 4 through the restrictor 3.
A conventional piezoelectric ink-jet printhead is shown in FIG. 2. FIG. 3 illustrates a cross-sectional view of the conventional piezoelectric ink-jet printhead in a lengthwise direction of a pressure chamber of FIG. 2. FIG. 4 illustrates a portion of a cross-sectional view taken along line A-A′ of FIG. 3.
Regarding to FIGS. 2 through 4, the conventional piezoelectric ink-jet printhead is formed by stacking a plurality of thin plates 11 to 16 and then adhering the plates to one another. More specifically, a first plate 11, on which a nozzle 11a through which ink is ejected, is formed and is the bottom of the printhead. A second plate 12, on which an ink reservoir 12a and an ink outlet 12b are formed, is stacked on the first plate 11. A third plate 13, on which an ink inlet 13a and an ink outlet 13b are formed, is stacked on the second plate 12. An ink supply hole 17, through which ink is supplied to the ink reservoir 12a from an ink container (not shown), is provided on the third plate 13. A fourth plate 14, on which an ink inlet 14a and an ink outlet 14b are formed, is stacked on the third plate 13. A fifth plate 15, on which a pressure chamber 15a, both ends of which are in flow communication with the ink inlet 14a and the ink outlet 14b, respectively, is formed and is stacked on the fourth plate 14. The ink inlets 13a and 14a serve as a passage through which ink is supplied to the pressure chamber 15a from the ink reservoir 12a. The ink outlets 12b, 13b, and 14b serve as a passage through which ink is ejected to the nozzle 11a from the pressure chamber 15a. A sixth plate 16 for closing the upper portion of the pressure chamber 15a is stacked on the fifth plate 15. A driving electrode 20 and a piezoelectric layer 21 are formed as a piezoelectric actuator on the sixth plate 16. Thus, the sixth plate 16 serves as a vibration plate operated by the piezoelectric actuator, and the volume of the pressure chamber 15a under the sixth plate 16 is varied according to the deformation of the vibration plate.
In general, the first, second, and third plates 11, 12, and 13 are formed by etching or press-working a metal thin plate, and the fourth, fifth, and sixth plates 14, 15, and 16 are formed by cutting a ceramic material having a thin plate shape. Meanwhile, the second plate 12 on which the ink reservoir 12a is formed, may be formed through injection molding or press-working a thin plastic material or an adhesive having a film shape, or through screen-printing an adhesive having a paste shape. The piezoelectric layer 21 formed on the sixth plate 16 is made by coating a ceramic material having a paste shape with a piezoelectric property and sintering the ceramic material.
As described above, in order to manufacture the conventional piezoelectric ink-jet printhead shown in FIG. 2, a plurality of metal plates and ceramic plates are separately processed using various processing methods, and then are stacked and adhered to one another using a predetermined adhesive. In the conventional printhead, however, the number of plates constituting the printhead is quite large, and thus the number of processes of aligning the plates is increased, thereby increasing an alignment error. If an alignment error occurs, ink is not smoothly supplied through the ink passage, thereby lowering ink ejection performance of the printhead. In particular, as high-density printheads have been manufactured in order to improve printing resolution, improvement of precision in the above-mentioned alignment process is needed, thereby increasing manufacturing costs.
However, the plurality of plates constituting the printhead are manufactured of different materials using different methods. Thus, a printhead manufacturing process becomes complicated, and it is difficult to adhere different materials to one another, thereby lowering production yield. Further, even though the plurality of plates may be precisely aligned and adhered to one another in the printhead manufacturing process, due to a difference in thermal expansion coefficients between different materials caused by a variation in ambient temperature when the printhead is used, an alignment error or deformation may still occur.